Evidence for simultaneous anxiolytic and aversive effects several hours after administration of sodium phenobarbitone to the rat.

Using a place conditioning paradigm, it was shown that the state experienced by rats 8 h after a 50-mg/kg dose of sodium phenobarbitone had aversive properties. However, at this same time, rats showed an increase in the percentage of time spent on the open arms of an elevated plus-maze, and an increase in the number of punished licks in a conflict test. These two effects are indicative of an anxiolytic action. It was therefore possible to demonstrate, simultaneously, an anxiolytic effect of sodium phenobarbitone and that it induced an aversive state. Conditioned place aversion could also be demonstrated 1 h after a 20-mg/kg dose of sodium phenobarbitone, but this dose was ineffective in the elevated plus-maze test of anxiety. These results provide further evidence that drugs that reduce anxiety do not necessarily have secondary positive reinforcing properties.